If a sending device and a receiving device are connected by multiple transmission channels (e.g., in the form of multiple data transmission lines) the data transmission rate between the sending device and the receiving device can be increased by bundling multiple transmission channels. The bundled transmission channels represent one logical transmission channel between the sending device and the receiving device, although the bundled transmission channels are in general separate physical connections which are spatially separated from each other.
The bundling of multiple transmission channels can be implemented in various ways, in particular on various layers according to the OSI layer model. For instance, in the case of the multilink point-to-point protocol (MPPP), the channel bundling is implemented on the network layer (i.e., the third layer according to the OSI layer model). Implementation of channel bundling on the first layer according to the OSI layer model, the physical layer, is advantageous, among other reasons, because such an implementation of channel bundling is independent of the specific protocols which are used on the higher layers according to the OSI layer model (i.e., it is transparent to these layers). Additionally, channel bundling on the physical layer is often technically simpler to implement than on higher layers according to the OSI layer model.
For these reasons, methods of bundling multiple transmission channels on the physical layer (also called bonding) have been developed, the bundled channels having a standard interface to the higher layers according to the OSI layer model. Examples of such implementations of channel bundling are the PMI aggregation function (PAF) bundling for Ethernet technology, in which Ethernet data packets are fragmented into smaller packets which are transmitted via the bundled transmission channels, and the IMA+ bundling for ATM technology, in which ATM cells are distributed to the bundled transmission channels and transmitted via them in such a way that the original sequence of cells can be restored in the receiving device.
However, neither PAF bundling nor IMA+ bundling define a specific form of a method and a facility for bundling multiple transmission channels on the physical layer. As illustrated in FIG. 6(a), a bundling facility 14 is often designed as a separate facility, which is connected to the transmission channels 11′-13′ to be bundled and divides a data stream into the transmission channels 11′-13′ to be bundled. However, the bundling facility 14 can also, as illustrated in FIG. 6(b), be designed as part of transmission channel facilities 11-13 to be bundled, of which at least one has an interface 15 to a facility which acts on a higher layer according to the OSI layer model (e.g., a media access controller (MAC)). However, if the transmission channel facilities to be bundled are separated in space, in the case of the implementation illustrated in FIG. 6(b) connections 17 are employed between the transmission channel facilities to be bundled to transmit sub-streams of the data stream to be transmitted via the transmission channels to be bundled from one transmission channel facility (e.g., 11) to another transmission channel facility (e.g., 12 or 13) and to thus implement the channel bundling.
FIG. 7 illustrates a specific example of data transmission using conventional bundling of two transmission channel facilities 11, 12 for the case that the bundling facility 14 is designed as part of the transmission channel facilities. Here the data to be transmitted via the transmission channels to be bundled is transmitted, for instance, via a first interface 15 between an Ethernet or ATM switch 18, which includes a media access controller (MAC) for each of the transmission channel facilities 11-13, and the bundling facility 14, which is designed as part of the first transmission channel facility 11. There the data is fragmented or defragmented, and a sub-stream of data is transmitted via the connection 17 from the first transmission channel facility 11 to the second transmission channel facility 12. Whereas the second transmission channel facility 12 can also have an interface 15 to the Ethernet or ATM switch 18, no data is transmitted via it, as illustrated by dashed lines. Instead, the transmission channel facilities 11 and 12 act as one logical transmission channel, which acts, to the Ethernet or ATM switch 18, as a facility on the first layer according to the OSI layer model.
However, depending on the specific form of the method and device for channel bundling, if the bundling facility is designed as illustrated in FIG. 6(b) or FIG. 7 as part of the transmission channel facilities, a physical connection between all pairs of transmission channel facilities to be bundled may be necessary. If, in the design of the data transmission device, maximum flexibility is to be preserved by the possibility of bundling arbitrary pairs of transmission channel facilities, the number of connections between transmission channel facilities to be bundled that are required to transmit sub-streams of data increases according to the square of the number of transmission channel facilities. In general, to bundle N≧2 transmission channel facilities, N(N−1)/2 connections between transmission channel facilities to be bundled are necessary, to transmit sub-streams of the data stream to be transmitted via the transmission channels to be bundled between the transmission channel facilities. Because of the quadratic increase of the number of required connections between transmission channel facilities to be bundled, for a large number of transmission channel facilities, such bundling of multiple transmission channel facilities is implemented at high cost.
For these and other reasons there is a need for the present invention.